The invention is directed to regulated optical amplifiers and optical transmission paths wherein these amplifiers are utilized.
Optical amplifiers are utilized in optical transmission networks as compensation for the fibre attenuation. A stable operation over further transmission paths, however, is only possible when modifications of the system parameters are compensated with the assistance of controls. The aggregate output powers of the amplifiers are regulated in previously employed wavelength-division multiplex (WDM) transmission systems. Given single-channel systems or paths having a constant number of channels, slow changes of the system parameters, such as changes due to temperature fluctuation or aging, are compensated rather well with this control concept.
When, however, the number of channels changes during operation, then aggregate output power regulation changes the levels of the individual WDM transmission channels. Such a level change can be fundamentally avoided by identifying the active channels and informing the control devices of the individual optical-amplifiers of the active channels identified. The control devices correspondingly adapt the rated value for the output level of the amplifier. Due to the different time constants, however, this level matching does not usually succeed without brief-duration fluctuations with which are connected considerable losses of transmission quality.
Another possible solution is comprised in regulating the individual amplifiers to constant gain (amplification). Such amplifiers are described in xe2x80x9cElectronic Lettersxe2x80x9d, Mar. 26, 1991, Vol. 27, No. 7, pages 560-561 and in xe2x80x9cElectronic Lettersxe2x80x9d Jun. 9, 1994, Vol. 30, No. 12, pages 962-964. In these circuits, the level fluctuations of the remaining channels"" given a change in the number of active channels"" are suppressed by keeping the gain constant. However, this control principle is also not suitable as a control concept for a transmission path having a plurality of amplifiers because slow changes in the path parameter accumulate and deterioration of the transmission quality results.
It is therefore an object of the invention to specify suitable amplifiers for optical transmission networks. Moreover, the transmission paths are to be fashioned such that the reception levels of the individual WDM channels remain constant even given a change in the number of channels.
This and other objects are achieved by a regulated optical amplifier circuit for use in wavelength-division multiplex signal transmission having an optical amplifier, a first control portion and a second control portion. The first control portion is configured to regulate the gain of the optical amplifier. Control behavior of the second control portion is significantly lower than the first control portion and the second control portion is configured to regulate an output power level of the optical amplifier according to an input reference value.
According to another aspect of the present invention, a regulated optical amplifier circuit includes an optical amplifier, a first control portion configured to regulate the gain of the optical amplifier and an input control device for inputting the rated value to the first control portion. The input of the rated value to the first control portion by the input control device is effected in order to set the gain of the optical amplifier. Additionally, the input control device receives a reference value and is configured to regulate power output of the optical amplifier by inputting a particular rated value input based on the received reference value.
In yet another aspect of the present invention, a transmission path for wavelength-division multiplex signals includes a plurality of amplifiers connected in a concatenated fashion and an input line for supplying a reference value to the plurality of amplifiers. The reference value is configured to respectively determine and desire output level for each of the plurality of amplifiers. Furthermore, each of the plurality of amplifiers includes a corresponding control device configured to adjust a respective gain of the corresponding amplifier in response to the supplied reference value.
An advantage of the inventive optical amplifier is that the gain regulation in the first control circuit works with a short time constant. Changes in the number of active WDM channels therefore have only a minimum effect on the output level. The second control circuit ensures that slow changes are leveled out. Given a change in the plurality of active channels, a corresponding change of the rated value of the second control circuit is effected on the basis of a local terminal inserted into the transmission path at the transmitter side or on the basis of a terminal (network node) of the reception side, so that the output level control is perceptible for only a brief-duration and minimally, if at all.
When a storage element is provided in the second control circuit, then it is possible to have this control circuit take effect only at specific times in order to modify the reception level or to deactivate it during a change in the number of channels.
In an alternative solution, the regulation of the output power either is effected in common for all amplifiers of a transmission path proceeding from the reception terminal or, given a corresponding, individual monitoring of the output levels, also separately via a correspondingly fashioned monitoring channel.
Due to the employment of an output level regulation, the amplifiers need only receive information about the plurality of WDM channels or a corresponding rated value.
The transmission paths equipped with these amplifiers can also level out slow changes in amplification caused by aging processes.
Additional advantages and novel features of the invention will be set forth, in part, in the description that follows and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combination particularly pointed out in the appended claims.